The invention relates to a puffer type electrical circuit breaker having a sealed casing made of moulded insulating material, filled with an insulating gas with high dielectric strength, notably sulphur hexafluoride, and comprising:
a pair of connection terminals passing through the wall of the casing,
a main circuit for the rated current to flow through having a fixed main contact and a movable main contact,
an auxiliary shunting circuit of the main circuit for breaking the current, and having a fixed arcing contact and a movable arcing contact, arranged in the same casing and the same gas as the main contacts, said main circuit being connected directly to the connection terminals, inside the casing extending along an adjacent trajectory transversely offset from and being shorter than that of the auxiliary circuit,
and a circuit breaker operating mechanism designed to separate the main contacts before the arcing contacts open.
A state of the art circuit breaker of the kind mentioned is described in French Pat. No. 2,441,916 and European Pat. No. 11,542 filed by the applicant. The insulating casing of the circuit breaker is oblong and is subdivided by a horizontal internal wall into two compartments superposed along the longitudinal axis. The main contacts separation zone is arranged in the lower compartment, whereas the breaking gap between the arcing contacts is located in the upper compartment. It can be noted in the middle area of the casing that the fixed main contact connection system is at the potential of the upper terminal, whereas the laterally juxtaposed movable arcing contact is at the potential of the lower terminal. The difference in potential causes a strong electrical field in this area, liable to affect the electrical insulation of the circuit breaker according to the value of the rated voltage used. The longitudinal offset of the main circuit and arcing circuit separation areas limites the performances and dielectric withstand of a circuit breaker of this kind.
The object of the invention consists in improving the dielectric withstand of a puffer circuit breaker having the main circuit and the arcing circuit arranged side by side inside the casing.